Kiwis may have to watch out for 'space junk' falling from the sky as an out-of-control Russian satellite orbits over the country over the next two days.

After a decade of planning and an estimated cost of more than $200 million (NZD), "Phobos-Grunt" was launched from Kazakhstan in November.

Its mission was to land on Phobos, a moon of Mars, and to release a satellite to send information back to Earth.

However, for unknown reasons the Russian agency lost communication control of it and as it travels on an elliptical earth orbit, said Department of Archaeology lecturer at Adelaide's Flinders University Dr Alice Gorman.


From tracking the craft, it is expected to fly over New Zealand several times between tomorrow and Monday and there was a chance of 'space junk' such as metals and other materials falling onto the country, she said.

"There are things that could fall - fuel tanks, robust metals like titanium and a few other components. There'll be some parts that survive re-entry."

Fuel and less robust metals were expected to melt and vapourise from from heat before re-entry, so were not a concern: "the risks, fortunately are low," said Dr Gorman.

There was only one recorded injury from falling space junk since the 1950s, she said.

An operational group was monitoring the orbit of the spacecraft as it passes over NZ several times.

The exact times it would cross over the country could not be pinpointed as it is dependent on the height of its orbit, solar activity and atmospheric conditions.

The final destination of the spacecraft, or what was left of it, was unknown but was predicted to be in the Atlantic.

'If anything is likely to survive the fall to Earth, it's the 11kg return capsule which has a heat shield and was of course designed for re-entry. But now it's still attached to the entire spacecraft, so how it will fare is hard to say."